IF-ELSE和SWITCH有什么区别？ [英] What is the difference between IF-ELSE and SWITCH?

问题描述

有人可以向我解释一下吗？

Can someone please explain this to me?

推荐答案

它们非常相似，但每个都有一些特殊功能。

They are pretty similar but each has a few special features.

切换

• 切换通常比许多嵌套更紧凑，如果没有，因此更具可读性


• 如果省略在两个交换机案例之间中断，您可以使用许多类C语言进入下一个案例。使用 if else 你需要一个 goto （这对你的读者来说不是很好......如果语言完全支持转到。


• 在大多数语言中，开关只接受原始类型作为键和常量作为案例。这意味着它可以由编译器使用非常快的跳转表进行优化。



• 目前还不清楚如何格式化 switch 正确。在语义上，这些案例是跳转目标（如 goto 的标签），它应该是向左刷新的。当你有大括号时情况变得更糟：

• switch is usually more compact than lots of nested if else and therefore, more readable
• If you omit the break between two switch cases, you can fall through to the next case in many C-like languages. With if else you'd need a goto (which is not very nice to your readers ... if the language supports goto at all).
• In most languages, switch only accepts primitive types as key and constants as cases. This means it can be optimized by the compiler using a jump table which is very fast.

• It is not really clear how to format switch correctly. Semantically, the cases are jump targets (like labels for goto) which should be flush left. Things get worse when you have curly braces:

case XXX: {
} break;

或者大括号是否属于他们自己的行？闭合支撑是否应该落后于中断？这有多难以理解？等等。

Or should the braces go into lines of their own? Should the closing brace go behind the break? How unreadable would that be? etc.

if-else

• if 允许复杂表达式处于条件状态，而switch想要一个常量


• 你不能不小心忘记 break 如果 s但你可以忘记 else （特别是在cut'n'paste期间）


• 它接受所有数据类型。

• if allows complex expressions in the condition while switch wants a constant
• You can't accidentally forget the break between ifs but you can forget the else (especially during cut'n'paste)
• it accepts all data types.

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